Days after his tragic death, Wahlberg tells The Hollywood Reporter Hoffman made him feel comfortable shooting their "Boogie Nights" kissing scene: "He was such a generous actor."

It's a depressing testament to Philip Seymour Hoffman's acting talent that so few people at January's Sundance Film Festival -- his final public appearance -- grasped how dangerously fragile a state he was in. There were moments as he plodded through the snowy streets of Park City, trudging from one publicity event to the next, hawking his two films -- God's Pocket and A Most Wanted Man -- when he seemed drained and distracted, a bit scruffy and more pasty-skinned than usual. But when he bound into THR's photo and video studio Jan. 18, munching on an apple and joking with photographers and reporters, he seemed healthy and happy as could be. Asked how he was holding up with the chaos of promoting two movies, he simply smiled. "There are definitely worse things I could be doing right now," he said.

Hoffman, of course, didn't look anything like a movie star. He wasn't tall. He wasn't slim. His hair seemed as if it had been combed with a blender. But days after his body was discovered in an apartment in New York's West Village -- a needle reportedly stuck in his arm, envelopes of heroin scattered about -- a long taken-for-granted fact was suddenly, tragically made clear: that at 46, he was one of the most savvy, precise and scarily committed actors of his generation. The evidence is overwhelming: his Oscar-winning performance in Capote, his Tony-nominated turns in True West, Death of a Salesman and Long Day's Journey Into Night and his dozens of other unforgettable roles, big and small, delivered in films as diverse as Boogie Nights, The Big Lebowski, Magnolia, Doubt, The Talented Mr. Ripley, Almost Famous, Cold Mountain, Charlie Wilson's War, Moneyball, The Master … the list goes on and on.

The grim details of Hoffman's last days are being pieced together. What is known at this writing is that his body was discovered at 11:30 a.m. Sunday, Feb. 2, by his friend, screenwriter DavidBarKatz. He reportedly had missed an appointment to pick up his three elementary school-aged children (with his longtime girlfriend, costume designer MimiO'Donnell), and Katz was concerned enough to ask the building manager to open the actor's apartment door. He found Hoffman slumped in the bathroom. Police later revealed that as many as 50 envelopes were found nearby, some marked with the words "Ace of Spades" in purple letters, others stamped with a red ace of hearts -- both well-known heroin "brands." Autopsy results have not yet been made public, but it is assumed the cause of death was an overdose.

Hoffman had been open about his struggles with substance abuse. In a 2006 interview with CBS' 60 Minutes, he was unabashed about his appetites. "It was everything I could get my hands on," he recounted of his early drug use. "I liked it all." But he entered rehab at 22, while earning his bachelor of fine arts from New York University, and later maintained he had been sober the next two decades. Cigarettes, which he chain-smoked during interviews, seemed his last remaining vice. In May, though, after legally prescribed painkillers triggered a slide back into addiction, he again entered rehab. This time, the program apparently didn't stick.

Boogie Nights (pictured above) wasn't Hoffman's first screen performance -- it was just the one that put him on the map. The Rochester, N.Y.-born actor (his mother is a family court judge, his father a former Xerox executive) got his start playing a rape-case defendant in a 1991 episode of Law & Order, then moved on to smallish parts in 1992's Scent of a Woman, 1994's When a Man Loves a Woman and 1996's Twister. But his role in PaulThomasAnderson's porn-set 1997 melodrama Boogie Nights -- playing Scotty J., a sexually confused boom operator -- really launched his career. In a film full of scene-stealing moments, Hoffman stood out with his self-loathing meltdown after a botched pass at Mark Wahlberg's Dirk Diggler ("I'm a fuggin' idiot. I'm a fuggin' idiot. Fuggin' idiot, fuggin' idiot, fuggin idiot …").

"We were both young and had only made a couple of movies," Wahlberg tells THR. "I had a scene where [we] had to kiss. It was one of those times when I was kind of uncomfortable with the part, but Phil made me comfortable. He was such a generous actor. Phil was fearless and selfless. We spent quite a bit of time together. We had a barbecue at my apartment in L.A., and Phil and all of us were running around having beers and lighting fireworks. The next day, I had an eviction notice on my door."

Among those who noticed Hoffman in Boogie Nights were other up-and-coming indie directors who began casting him in what would become touchstone films of the late 1990s and early 2000s. The Coen brothers hired him to play Brandt, the officious assistant in 1998's The Big Lebowski; AnthonyMinghella cast him as frat boy FreddieMiles in 1999's The Talented Mr. Ripley (the late director described Hoffman as an actor "cursed by his own gnawing intelligence"); CameronCrowe picked him to play iconic music critic LesterBangs in 2000's Almost Famous ("It became the soul of the movie," wrote Crowe of Hoffman's performance in a remembrance on his website. "Between takes, Hoffman spoke to no one. He listened only to his headset, only to the words of Lester"). Before long, Hoffman was a fixture on indie screens, usually as a supporting character but always making himself memorable.

Then, in 2005, one of Hoffman's childhood pals, BennettMiller (the two met as teenagers at summer drama camp), cast him as the lead in a low-budget biopic about an idiosyncratic 1950s author with a famously shrill voice. Capote wasn't merely a breakthrough for Hoffman; it transformed his reputation as an actor and ultimately won him that Oscar. He threw himself into the role so completely, he refused to break character during the entire 36-day shoot. "If you are running a race, you don't want to stop in the middle and have to start again," explained Hoffman of his method shortly after the film's release. "I had to keep a certain sense of the voice and quality and these things because if I let it go, it was too much energy to get it back up again."

Says GeraldClarke, who wrote the biography on which Miller based the film: "I knew Truman Capote very well, and sometimes when I was watching Philip on the screen, I thought I was watching Truman. I saw the movie at a small screening; Philip was sitting behind me. He came up afterward, and we hugged, and I said, 'You are Truman Capote.' But Philip, like Truman, had no shell, the protective covering most people have. He was too open to every vibration."

Hoffman was not in love with being famous. He dressed more like a cabdriver than a celebrity. During interviews with the press, he mumbled and fidgeted. Like many great actors, he appeared painfully itchy in his own skin. It was only when he slipped into someone else's personality -- whether it was a violinist in 2012's A Late Quartet or the leader of a futuristic rebellion in TheHunger Games franchise -- that he truly seemed to come alive. (Lionsgate says Hoffman's part in the next two installments mostly had been filmed before his death, though sources say one key scene in the fourth film had not been shot.)

"Not everybody who becomes [a movie star] wants it," he told me in 2007 when I was interviewing him for a story on Charlie Wilson's War (in which he co-starred with two of the biggest, TomHanks and JuliaRoberts). "Some of them want it, but not all of them. It's not fun." One of the reasons Hoffman continued to act onstage was that he saw it as an antidote to soul-corrupting Hollywood-style fame. It's part of the reason he stayed in New York at a point in his career when a lot of other actors would have set up shop in Malibu or Silver Lake. It's why he took the subway home after performing on Broadway. Why his neighbors in the West Village often spotted him on a scooter taking his kids to public school.

However modest his lifestyle, though, Hoffman was in every sense a star. Before his lapse back into drug use, he seemed on the verge of another creative burst. He was set to direct Ezekiel Moss, starring Amy Adams and Jake Gyllenhaal. He was in talks with Wahlberg about starring together in American Desperado, to be directed by Peter Berg. And he had shot a pilot for a Showtime series titled Happyish, about an unhappy middle-aged man, that was on the verge of going into production (Showtime released a condolence statement after Hoffman's death, but there was no word on whether it plans to recast the series or drop it). Hoffman would have disagreed, no doubt violently, but he seemed as close to anyone to having it all.

"If you stop to think about a life and the length of it," he said in that 2007 interview, "you can't have everything. You never can. That's not a Hollywood thing or an actor thing -- that's a life thing. You think you can work at that job and that other job and coach Little League and be a teacher and whatever, but you can't have everything. Life throws in things against your best wishes."